Raster input scanning technology has progressed rapidly in recent years, particularly in data entry applications. With the scanning arrays longer, and comprised of greater numbers of photosites than ever before requiring only a single array to read the sagittal (x axis or fast scan direction) of the document, scanning speeds have greatly increased. The entry of data to data processing systems through raster input scanning devices has become an attractive goal.
While data processing and scanning arrays have become substantially less expensive, the exacting mechanical alignment required for the scanning arrays and optics remains a significant cost factor in the construction of raster input scanning devices. Without exact mechanical positioning of the scanning arrays with respect to the optical system and input information handling devices, the scanner is inexact, and data errors may result. While a well constructed device may be aligned to within a few tenths of a percent of the desired position, a careless alignment will cause significant problems. As an example, a photosite array housing and support may require several adjustments, including adjustments to slow scan (y-axis) and fast scan direction, tilt, magnification, focus and height requiring separate parts adjustable in each direction. Even with excellent factory quality controls, disturbance in the field may ruin a careful factory alignment. A self aligning device operative to avoid certain of these mechanical adjustments would improve this problem significantly.
U.S. Pat. No. 4,149,091, assigned to the same assignee as the present invention, and incorporated herein by reference, describes a system for aligning a plurality of offset and overlapping arrays by measuring and storing information in a device memory regarding the array positions with respect to each other, and using the stored information as offset values in processing the data entered into a processing system through the raster input scanner. The information regarding the position of the sensor arrays necessary for this system is acquired by microscopically measuring the arrays and storing the information in a memory as a vernier scale which tells the scanning device when to switch from array to array.
The Xerox Disclosure Journal "Raster Scanner Alignment Techniques", Vol. 5, No. 3 (May/June 1980) appears to show an calibration method for determining offsets required to correct misalignment. The y-axis is adjusted by choosing the array offsets along the y-axis, and the x-axis is adjusted by choosing the bit offsets along the x-axis. The primary thrust of the discussion relates to the provision of a particular type of test document for improved calibration use.
Japanese Patent Document No. 59-63873 provides a picture input device in which a rotary encoder integrally mounted with the line sensor is used as a range finder whereby for each movement of the line sensor a predetermined distance a pulse is directed to a controller.